Development and optimization of a naphthoic acid-based ionic liquid as a “non-organic solvent microextraction” for the determination of tetracycline antibiotics in milk and chicken eggs

• Novel naphthoic acid-based ionic liquid was synthesized and characterized.
• “Functionalized ionic liquid-based non-organic solvent microextraction (FIL-NOSM)”.
• Utilization of this ionic liquid enhanced recovery and avoided pH adjustment.
• Central composite design was applied to optimize operational factors.
• Low LODs and high recoveries for tetracyclines by FIL-NOSM method in foods.

In traditional ionic liquids (ILs)-based microextraction, ILs are often used as extraction and dispersive solvents; however, their functional effects are not fully utilized. Herein, we developed a novel ionic liquid 1-butyl-3-methylimidazolium naphthoic acid salt ([C4MIM][NPA]) with strong acidity. It was used as a mixed dispersive solvent with conventional [C2MIM][BF4] in “functionalized ionic liquid-based non-organic solvent microextraction (FIL-NOSM)” for determination of tetracycline antibiotics (TCs) in milk and eggs. Utilization of [C4MIM][NPA] in FIL-NOSM method increased extraction recoveries (ERs) of TCs by more than 20% and eliminated the pH adjustment step because of its strong acidity. Under optimized conditions based on central composite design, the ERs of four TCs were 94.1–102.1%, and the limits of detection were 0.08–1.12 μg kg−1 in milk and egg samples. This proposed method provides high extraction efficiency, less pretreatment time and requires non-organic solvents for determination of trace TC concentrations in complex animal-based food matrices.